This invention relates to connectors for attaching electrical cable to a circuit board. More particularly, the present invention provides a method and apparatus for easily and securely attaching an electrical cable to a circuit board.
One problem encountered in a variety of industries today is the connection of an electrical cable to a circuit board. Circuit boards typically comprise some form of electric circuitry and can be used in a variety of conventional devices and processes. Circuit boards are typically made of a combination of materials such as metal traces positioned on relatively delicate substrate material, where the substrate material is often referred to as a dielectric. The electrical cables that need to be attached to the delicate circuit boards are often inflexible. The inflexibility of the cable and delicate nature of the circuit board make it difficult to create a connection between the cable and the circuitry on the circuit board that is mechanically and electrically secure.
This problem is particularly apparent in the field of antennas. Antennas, and particularly cellular antennas mounted on a pole at a base station, often have spatial constraints that make it desirable to construct an antenna of compact size. Aesthetic and environmental concerns can also control the size and shape of the antenna, which in turn impact the construction and assembly of the components within the antenna. The difficulty of assembling the antenna components in a small area is further complicated by physical constraints that ensure the components function properly. This difficulty is particularly acute in that portion of the assembly process where a power cable is connected to the dielectric circuit board within the antenna. Typically, an intermediate coaxial cable is used to connect an external power cable and the circuit board. Because the intermediate power cable is relatively short and stiff, it is difficult to achieve a secure connection with the circuit board. One common problem resulting from poor connections is degradation of the electrical signal caused by stresses in the connection between the power cable and the circuit board. In some instances the dielectric circuit board will crack or break because of its delicate nature.
The key to solving these problems lies in the design of the connector and how the connector is attached to the intermediate power cable and the dielectric circuit board. Existing connectors are difficult to work with in confined spaces and often produce connections with undue stresses that adversely affect the antenna. Attempts have been made to manufacture better connectors. Examples of more complex connectors are illustrated in U.S. Pat. No. 4,737,111, entitled xe2x80x9cRF Connector for Use In Testing a Printed Circuit Board,xe2x80x9d and U.S. Pat. No. 6,106,304, entitled xe2x80x9cCable Connecting Head for Connecting to an Integral Circuit Board.xe2x80x9d However, there are limitations with the designs taught in these patents. First, the connectors do not facilitate simple and secure connection of the two conductors of a coaxial cable to a circuit board. Typically, it is necessary to solder the outer conductor to the circuit board ground and to solder the inner conductor to a trace connected to the circuit. The connector designs of the prior art do not allow for easy access to the outer and inner conductor for soldering. Second, the prior art connectors are expensive in that they require modification of the circuit board (drilling holes) and machining of a complex connector device. These additional costs make the designs prohibitive. Third, the designs taught in these two patents require turning and manipulation of the connector device to attach it to the circuit board. Maneuvering the connector device is difficult given the compact structure of cellular antennas.
Two other types of connectors that are generally used for this type of application are illustrated in FIGS. 1, 2, and 3. The connector shown in FIG. 1 is an example of a standard connector. The standard connector 2 connects intermediate cable 3 to circuit board 1. The intermediate cable 3 is then connected to an external power cable (not shown) via a DIN connector 4. The DIN connector is attached to the antenna tray 5, usually with rivets 6. The intermediate cable 3 comprises an outer conductor 7 and an inner conductor 8. The intermediate cable 3 is inserted into the distal hole 9 of the standard connector 2 such that the inner connector 8 protrudes from the proximal side of the standard connector 2. The outer conductor 7 can be soldered to the standard connector 2 and the inner conductor 8 can be soldered to the circuit board 1 at the microstrip trace line 10. The standard connector 2 also comprises two top stubs 11 and 12 and two bottom stubs 11xe2x80x2 and 12xe2x80x2 (not shown). The connector 2 is typically soldered to the circuit board 1 at stubs 11, 11xe2x80x2, 12, and 12xe2x80x2.
The other type of conventional connector is called a clamp nut connector. An exemplary clamp nut connector, as manufactured by Amphanol Connectors, Inc. in Allentown, Pa., is shown assembled in FIG. 3 and unassembled in FIG. 2. The clamp nut connector 20 comprises a clamp nut 21, a threaded nut sleeve 22, a ferrule 23, and a connector assembly 24. The process for connecting the intermediate cable 25 with a clamp nut connector differs somewhat from the process for a standard connector. With the clamp nut connector, the intermediate cable 25 is fed through the clamp nut 21 and the threaded nut sleeve 22. The ferrule 23 is then attached to the end of the intermediate cable 25 and soldered to the cable""s outer conductor 26. The connector assembly 24 is inserted onto the edge of a circuit board 33 such that upper stubs 29 and 32 rest on the top of the circuit board 33 and the lower stubs 30 and 31 are beneath the circuit board 33. Each stub 29, 30, 31, and 32 is soldered to the circuit board 33 securing the connector assembly 24. The ferrule 23 is then inserted into the connector assembly and secured by tightening the clamp nut 21. Finally, the inner conductor 27 can be soldered to the circuit board 33. The problem with the clamp nut connector is that it requires the machining of several more parts than the standard connector. These additional parts add to the cost of the connector and also add additional steps to the antenna assembly process. Furthermore, manipulation of the clamp nut 21 in the confined space of an antenna system also causes unwanted movement and stress on the solder connections with the circuit board 33.
The rigid nature of the intermediate cable 3, 25 causes stresses in the various solder points of the connection. These stresses can be exacerbated by the fact that the shape of the standard connector 2 and the clamp nut connector 20 make it difficult to form secure solder joints. The resulting stresses can adversely affect the performance of the antenna. In an ideal antenna manufacturing process, the first two steps would involve attaching the DIN connector 4 to the antenna tray 5 and attaching the intermediate cable 3, 25 to the DIN connector 4. Then later in the manufacturing process, the intermediate cable 3, 25 would be attached to the circuit board 1, 33 via a connector.
Using a standard connector 2 or a clamp nut connector 20, the actual antenna manufacturing process occurs in the reverse order of the ideal process. The structure of the conventional connectors and the compact spatial constraints of cellular antennas require that the intermediate cable 3, 25 be connected to the circuit board 1, 33 first. Subsequently, the intermediate cable 3, 25 is bent and fed into the cylindrical opening of the DIN connector 4. The process of bending the intermediate cable 3, 25 and attaching it to the DIN connector 4, increases the problems associated with stresses accumulating in the solder connections at the connector.
In view of the foregoing, there is a need in the art for a connecting device that is inexpensive to manufacture and simple to use. Specifically, there is a need for a connector that comprises a single body that can be cheaply produced in large quantities. There is a further need for a connecting device that is compact and does not require significant manipulation in view of the compact design of an antenna. There is also a need for a connecting device that will adequately support connections between an electrical cable and a circuit board while minimizing the stresses in those connections.
The present invention comprises a method and a device for facilitating the connection of a cable to a circuit board. The present invention employs a connector having a simple design that will be inexpensive to manufacture. Simplifying the design of the connector streamlines the antenna assembly process. The design of the connector allows a manufacturer to create secure connections between the cable and circuit board while minimizing manipulation of the connector.
In one aspect, the invention comprises an apparatus for securing an electrical cable to a circuit board. The apparatus is a single-body, hollow half-cylinder shaped connector with at least one upper flange and at least one lower flange. The connector slides onto the edge of a circuit board so that the circuit board fits between the upper flange and the lower flange. Solder can be applied to attach the flanges of the connector to metal connection pads, metal traces, or other like structures on the circuit board. The connector comprises a semi-circular inner surface shaped to receive the cable. The connector is designed so that an inner conductor of the cable can rest on the circuit board and be soldered to the circuit. The connector can also have an aperture in its semi-circular tube portion for observing the soldering of the cable to the connector.
In another aspect, the invention comprises a method for attaching a cable to a circuit board using a connector. The method involves attaching to the edge of a circuit board a half-cylindrical shaped connector with a C-shaped groove. Flanges extending from one end along the axis of the connector fit above and below the circuit board. The connector""s flanges can be soldered to the upper and lower surfaces of the circuit board. Once the connector is secured to the circuit board, its semi-circular design facilitates placement of the cable onto the inner surface of the C-shaped groove of the connector with little manipulation. The cable can then be soldered to the connector and the circuit board with minimal stress on the connection points.
These and other aspects of the invention will be described below in connection with the drawing set and the appended specification and claim set.